1. Field of the Invention
The present invention relates to a vibration actuator having a piezoelectric element and a drive unit including the vibration actuator.
2. Description of Related Art
A vibration actuator including a piezoelectric element has been known. For example, Japanese Unexamined Patent Publication No. 2005-94956 discloses a vibration actuator.
The vibration actuator according to Japanese Unexamined Patent Publication No. 2005-94956 includes an actuator body including a piezoelectric element and driver elements attached to the actuator body.
The actuator body includes a plate-like piezoelectric element having a lengthwise direction. When AC voltages whose phases are different from each other are applied to two pairs of electrodes aligned along diagonal lines of the piezoelectric element, the actuator body generates longitudinal vibration in the lengthwise direction of the piezoelectric element (so-called stretching vibration) and bending vibration in the widthwise direction of the piezoelectric element (so-called transverse vibration) in harmony. As a result, driver elements make a circular motion, i.e., an elliptical motion, on a plane including the lengthwise and widthwise directions of the piezoelectric element.
The thus-configured vibration actuator is provided between a stationary body and a movable body arranged to be movable relative to the stationary body. To be more specific, the vibration actuator is fixed to one of the stationary body and the movable body, while the driver elements are in touch with the other one of the stationary body and the movable body (hereinafter referred to as a touched body). In this state, the vibration actuator is operated such that the driver elements make the circular motion as described above. Then, the driver elements press the touched body with increased friction during a certain part of the circular motion, while they come out of contact with the touched body or reduce the friction on the touched body during another part of the circular motion. When the driver elements press the touched body during the circular motion, a driving force is transmitted to the movable body through the friction between the driver elements and the touched body. Thus, the movable body is moved in a predetermined direction.
The vibration actuator disclosed by Japanese Unexamined Patent Publication No. 2005-94956 achieves size reduction by baking the driver elements and the piezoelectric element in one piece.